Process of making propellant powders



Patented Apr. 24, 1934 assen ATENT @Fiifi raooass or MAKING PROPELLANT POWDERS George A. McBride, Alton, Ill., assignor to Western Cartridge Company, East Alton, 111., a corporation of Delaware No Drawing. Application November 14, 1930 Serial No. 495,672

'14 Claims.

This invention relates to propellant powders, and more particularly powders of the type which are surface-treated -with a deterrent to retard the initial combustion rates.

* One of the objects of this invention is to provide a process of surface-treating propellant powders, and more particularly double base propellant powders adapted to improve the ballistic characteristics of such powders.

Another objectis to provide a process of the character described whereby the application of the deterrent to the powder grain can be controlled to secure the desired application.

Another object is to provide a process whereby the gravimetric density of a powder and more particularly a surface-treated powder, is indecreased, restored, or controlled.

Further objects will appear from the detail description, in which will be described an illustrative embodiment of this invention; it is to be understood however that this invention is susceptible of various other embodiments.

In the surface treatment of propellant powders with a deterrent, difficulty is experienced in securing the desired uniform distribution of the deterrent on the powder grain, and it is especially dimcult to secure uniformity of the application of the deterrent td the various grains of a. batch. Moreover, since the deterrent employed is usually a solvent or gelatinizer for the powder grain to be surface treated when the surfaces of the powder grains become softened through the action of the gelatinizing agent, the grains tend to stick together. These aggregates do not permit the automatic volumetric measuring devicesin the loadingmachines to operate satisfactorily so that variations in the weight of charge are encountered which give rise to erratic ballisticresults. While a deterrent may be applied in a solvent, dimculty'is experienced in not only controlling the amount and penetration of the (.eterrent to be taken up by each grain, but where the vehicle employed is also a solvent for the powder grains these again tend to stick together. Generally stated in accordance with this invention, the powder grains are treated with a deterrent while in a state of suspension. In accordance with one embodiment of this invention,

the deterrent is emulsified with a suitable liquidwhich is preferably a non-solvent for the powder grains; such a liquid is water, whereby a water emulsion of the deterrent can be made. In order to secure the addition of a predetermined amount of deterrent to powder grains, the powder grains are treated with a predetermined amount of the deterrent in the emulsified state until the deterrent is taken from the emulsion by the powder grain. In accordance with one embodiment of this invention, the powder grains are agitated in an emulsion of the deterrent and containing a predetermined amount of the deterrent until the liquid with which the deterrent is emulsified clears. Where the deterrent is a liquid at ordinary temperatures, it can simply be mixed with, for instance, water, until an emulsion is secured; where, however, the deterrent is a solid at Wordinary temperatures, it is heated to its melting point, either previous or after its addition to the liquid, such as water, and the treatment of the powder with emulsion is, therefore, carried out at approximately the melting pointof the deterrent. In such a "case, after the liquid has cleared, additional liquid may be added and the agitation continued, however, at a reduced temperature,

In order to generally accomplish the objects of this invention, the deterrent may be one of the usual ones employed for that purpose; A deter rent which has been found particularly useful is diamyl-phthalate; a related deterrent, such as dibutyl-phthalate, may also be employed. Both, 30

of course, are active solvents for nitrocellulose and practically non-volatile. Moreover, waxessuch as carnauba dinitro-toluene and the related mononitro and trinitro-toluenes may also be employed.

In the surface treatment of powder grains, and more particularly in the surface-gelatinizing of apowder with a deterrent, as heretofore described, it is found that the gravimetric density is decreased generally by the swelling of the surface of the grain to roughen or curl the same. This affects considerably the loading character of the powder and the amount which can be charged into a shell of a given capacity. In accordance with this invention, therefore, the powder is sub# Q jected to treatment for the purpose of restoringjl increasing or controlling the gravimetric density so as to reduce the curlof the surfaces of the grains. This reduction of curl may be descriptively termed a smoothing of the general contour 'of the grains although it will be understood that the surface irregularities need not be eliminated to accomplish this. This is accomplished in accordance with one embodiment of this invention by treating the grains at a temperature-and for a period sufiicient, and in a suitable medium or vehicle such as water, so as to complete "the gelat nization of the surfaces of the grains. Many of the advantageous features of this invention maybe secured by the surface treatment grain containing 15% nitro-glycerine is surface treated with diamyl phthalate in the following manner: A water emulsion is formed with the proper amount of the deterrent using, for instance, 5 parts of the deterrent relative to 94 parts of the powder. Into this emulsion the powder grains are dumped, agitation being con- .tinued until no cloudiness of the water is pre-' ceptible, that is, until the deterrent has been completely taken up by'the powder grains. Because of the finely divided, condition, almost colloidal,

of the deterrent in the water, distribution is ideal,

and the deterrent, because of its efflc'ient gelatinizing properties is attracted to the surfaces of tlze powder grains. As the deterrent droplets a e picked up, the surface of the powder grains are softened; however,- the presence of the water'very emciently cushions each grain from the others until gelatinization has been completed.

Where the gravimetric density of the powder has been decreased by the treatments heretofore described, the same is restored in the following manner: The powder is placed in water and held at C. for about fifteen minutes. Upon drying it is found that the gravimetric density of, for

instance, the intro-cellulose-nitro-glycerine powder surface treated with D. A. P. is restored from .498 to .530. Upon storage for an extended period, this gravimetric density is not'changed materially. The process is believed to be one of effecting complete gelatinization, thereby smoothing the contour of the grain to reduce its e fiec tivesize. I

Where the deterrent is dinitro; toluene instead ofdiamyl phthalate, it is found that about twice the amount of deterrent is required. Now, DNT at ordinary temperatures is a solid; accordingly,

the process is varied to the following extent: The

amount of water required is heated to about 95 C. andthe DNT allowed tomelt inthis water. Sufiicient agitation is then applied to completely distribute themolten DNT throughout thewater, so as to form an emulsion therewith. The powder when added very read ly picks up the very. tiny globules of DNT due perhaps to the accelerated gelatinization of nitro-cellulose at elevated tem-' peratures. Agitation at this temperature is continued until the water is clear, which occurs in most cases between one and five minutes. Thereafter more water may be added or the container may be externally cooled so that the temperature is reduced to about 60 C and agitation is continned at this temperature for about twenty-five minutes.

Whatever deterrent or process is employed, the

water is easily removed by centrifuging and drydoublebase powders, someof its features are of to the desired extent. It has been found that close control is possible with this process, and it has the further advantage in that it requires the use of no material which must be removed, except the water, which can be readily abstracted. Storage even at 50 C. carried out with this treated powder shows that it is remarkably stable. The process of restoring the gravimetric density is ad-' vantageous, for the charge which can be loaded into a shell of a given powder capacity can'be increased to a maximum.

Powder prepared in accordance with the process embodying this invention is particularly suitable for small calibre rifie cartridges, in that it develops a maximum velocity with minimum pressures; thus when employedin 22 calibre long rifle cartridges, a mean charge of, approximately 2.44 grains develops a mean velocity between 1200 and 1300 ,feet per second with a mean pressure of approximately 13,500 pounds per, square inch. In order tosecure some of the advantageous features of this invention, the grains may be treated with a deterrent while in a state of suspension in a medium other than a liquid; thus t e grains may be caused to pass through a dense ist of a deterrent, such as diamyl phthalate, by generating such a mist'by a spray of the heated deterrent. While this results in a rather eflicient distribution of the deterrent over the powder grains, it is not'as advantageous as where an emulsion of the deterrent is employed; for in the latter, although thejsurfaces of the grains are softened by the deterrent, the presence of the liquid with which the deterrent is emulsified very efliciently cushions each grain from the others until gelatinization has been'completed, so that sticking together of thegrains is avoided.

It will be understood that while this invention is particularly applicable to the -'treatment.of

advantage'in the surface treatment of nitrocellulose powders and smokeless powders generally. -Furthermore, the process is not necessarily confined to the use of materials which melt below the boiling point of water because other substances which have a higher melting point can be conveniently used provided they are first dissolved in some suitable solvent. Instead of forming an emulsion using the melted deterrent at .a temperature near 100 C., it may be found convenient to first dissolve the deterrent in some suitable solvent such as benzol. In this case an emulsion is then prepared comprising water as the continuous phase and the benzol solution of the wax or deterrent as the discontinuous phase. It will further be understood that various features and subcombinations are of utility and may be employed .without reference to other features and subcombinations; that is contemplatedby and is within the scope of the appended claims. It will be further understood that various changes g may be made in details without departing from the spirit of this invention; it is, therefore, understood that this invention is not to be limited to the specific details described. 4 Having thus described the invention, what is claimed is: 1. In the art of making propellant powders, the process comprising, treating powder grains with an emulsion of a solvent of low volatility. I 1 5 2. In the art of making propellant powders, the process comprising, treating powder grains with a deterrent emulsified with anon-solvent for the powder grains. v v

3. In the art of making propellant powders, the 150 process comprising, treating powder grains with a water emulsion of a deterrent.

4. In the art of making propellant powders, the

' process comprising, treating powder grains with an emulsion 01' a solvent of low volatility until the deterrent is taken from the emulsion by the powder grains.

5. In the art of making propellant powders, the process comprising, agitating powder grains in an emulsion of a solvent of low volatility.

6. In the art or making propellant powders, the process comprising, agitating powder grains with a predetermined amount of a deterrent emulsified with a liquid which is a non-solvent for the grain until the emulsion clears.

'1. In the art of making propellant powders, the

process comprising, treating powder grains with an emulsion of a deterrent approximate the melting point of the deterrent.

8. In the art of making propellantpowders, the process comprising, agitating powder grains with 1 a predetermined amount of a deterrent emulsified with a liquid until the emulsion clears, adding additional of the liquid and continuing the agitation.

9. In the art of making propellant powders, the

, the action of the suspension.

l3."In the art of making propellant powders, the process comprising, suspending a deterrent in a treating bath, exposing powder grains to the action of the suspension at a temperature approximate the melting point of the deterrent.

14. In the art or making propellant powders, the process comprising, suspending a solvent of low volatility in a treating bath, and exposing powder grains to the action of the suspension.

GEORGE A. MCBRIDE. 

